The benefits of delivering drug-loaded prostheses to patients are becoming well known. Studies have shown the effectiveness of delivering the correct drug dose density on coronary stents to prevent restenosis by application of, for example, paclitaxel or rapamycin. Numerous processes have been proposed for the application of such a coating including: soaking or dipping the implantable device in a bath of liquid medication, soaking in an agitated bath, introducing heat and/or ultrasonic energy in conjunction with a medicated bath, and spraying the medication by way of pressurized nozzles.
It is known to use ink-jet technology to apply a liquid to selected portions of a surface of a medical device such as a stent. An ink-jet nozzle moves with respect to the surfaces of the stent to be coated with the aid of a motion control system. In one configuration, the ink-jet nozzle moves along a linear track over the surface of the stent. The stent is rotated in order to present the surface to the ink-jet nozzle. The combination of the rotatable stent and the movable ink-jet nozzle allows for coating to be placed almost anywhere on the surface of the stent.
As the coating must be precisely applied, there are various known methods for controlling the accuracy of the coating placement so that only the stent is coated and not other parts. A real-time picture can be taken with a camera to determine the position of the ink-jet nozzle in relation to the prosthesis. Based upon the feedback of nozzle location, the ink-jet applicator can be controlled by coordinating the activation of the spray with the movement of the ink-jet nozzle, and/or with the movement of the prosthesis. The accuracy of the coating apparatus is a key to its successful operation.